The astonishing claim was made by Tim Collett of the United States Geological Survey at last weeks national meeting of the American Chemical Society. Collett told the gathering that, to the naked eye, clathrate hydrate (CH) looks like everyday ice but, as well as being partly made of water, the molecules are also organised into “cages”, which trap individual molecules of methane.

Remarkably, a new method of extracting the methane and ’swapping’ it with carbon dioxide could turn the substance into a revolutionary carbon-neutral fossil fuel.

The US Department of Energy is now working with the oil company ConocoPhillips on a field trial in Alaska (pdf), to test whether the technique can be scaled up.

According to Ray Boswell of the US National Energy Technology Laboratory, “A lot of countries are getting very serious about this. Something that used to be more hype than reality is becoming something people are seriously talking about.”

However, the technique is not without its critics, Neil Crumpton of Friends of the Earth said, “It’s a technology we think is best avoided. The US should be focusing its efforts on concentrated solar power in its southwestern deserts.”